NON-NATIVE PLANTS on SOUTH GEORGIA Season Report 2018/19
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NON-NATIVE PLANTS ON SOUTH GEORGIA Season Report 2018/19 NON-NATIVE PLANTS ON SOUTH GEORGIA Season Report 2018/19 Kelvin Floyd Indigena Biosecurity International This report was prepared by Indigena Biosecurity International Limited for the Government of South Georgia and the South Sandwich Islands April 2019 PO Box 54, Nelson, New Zealand. www.indigena.co.nz INTRODUCTION Non-native plant management during the 2018/19 season focused on undertaking actions to implement the ‘South Georgia Non-Native Plant Management Strategy 2016–2020’. Management action was taken to address priority non-native plant species and high priority sites. Further surveys were carried out to fill gaps in distribution data. There are now 82 non-native plant species recorded from South Georgia. Of these, 35 species are historic and presumed extinct, 3 are widespread and naturalised, and 5 are common locally. There are 36 species (Class One) that are managed on a zero population density basis (i.e. plants which may be present but are controlled before they set seed). Three research species require more information to classify. Although there were fewer temperature extremes in 2018/19 than in the previous season, rainfall was higher. In response to the warm 2017/18 summer some species produced more seedlings than usual this year. Lower than usual seal numbers this year meant some plants normally trampled were visible this season. Lobelia pratiana (berry-lobelia) has now been reclassified as a Class Two species due to the documented increase in its geographical distribution as it recovers from reindeer grazing. A new species (Rumex acetosa) to the island was found near Husvik whaling station and will be formally identified by the Royal Botanical Gardens at Kew.. Non-native plant species classes Class Description Class One – Priority species; require species-led control at the island-wide level, to control Species-Led all plants before they reach maturity. All sites with these species have a 'Site Tag' in the Weeds Database to enable management of follow-up visits. Class Two – Species of moderate distribution, requiring site-led control. Priority Site-Led populations are those at high-use visitor sites, and sites with small infestations where control will reduce further dispersal. Class Three – Species which are widespread and abundant, and require management at Site-Led high-use visitor sites and at some remote outlier sites where appropriate. Research More information required before classification. Non Native Plants on South Georgia Season Report 2018/19 Page 3 WORK UNDERTAKEN THIS SEASON This season the field team consisted of Kelvin Floyd (team leader), Sally Poncet, Ken Passfield, Jörg Kluge and Pamela Quilodran. Field work for the Darwin Initiative project ‘Securing South Georgia’s native habitats following invasive species control’ was also undertaken in association with non-native work this season by the team. Kelvin and Pamela arrived at King Edward Point(KEP) on FPV Pharos SG on 22rd December and began work locally around the base and Grytviken. Sally and Ken arrived at Husvik on 17th January via the FPV Pharos SG and carried out control of Class One and Two species in the Stromness Bay area including a half day on Grass Island supported by FPV Pharos SG. They returned to KEP on 27th February on a GSGSSI/BAS jet boat then went to Sorling Valley hut the following day to undertake work at Ocean Harbour and Hound Bay, returning to KEP on 4th March. They departed South Georgia on 7th March on FPV Pharos SG. Jörg Kluge joined the team at KEP on 2nd February, arriving on the cruise ship MV Fram . Kelvin, Pame and Jörg undertook work on Thatcher Peninsula near KEP with a short trip to Corral Bay hut to carry out control at Godthul and Reindeer Valley on Barff Peninsula. Kelvin departed on 7th March on FPV Pharos SG. Pame and Jörg departed on 11th March on HMS Clyde. Summary: 846 square metres of Class One species were treated this year compared to 2,733 square metres last season showing a marked decline in plant coverage at treated sites. 10,976 square metres of Class Two species were treated this season. 26 management units were visited this season for both control and surveys. Rumex acetosa (common sorrel) was found in the Karakatta Valley near Husvik whaling station, a first record for the island. Samples have been sent to Royal Botanic Gardens Kew. Herbicide usage and species details were recorded daily with all information entered into the South Georgia Plants Database. Non Native Plants on South Georgia Season Report 2018/19 Page 4 SOUTH GEORGIA NON-NATIVE PLANT STATUS 2017/2018 Species have been classed following the Non-Native Plants Strategy and are separated into each class below with a summary for each species. A full species list is presented at the end of this report CLASS ONE SPECIES Each species summary includes a graph showing total plant coverage treated in square metres for each control season. Class One locations visited 2018/19 Non Native Plants on South Georgia Season Report 2018/19 Page 5 Achillea millefolium yarrow No plants were found at the existing sites this season. Another small site was found near the Husvik whaling station in an area normally trampled by seals. Spread is vegetative as the species is not known to flower or set seed at South Georgia. 25 20 20 20 15 10 Coverage sq m sq Coverage 5 3 1.5 0.08 0.01 0.01 0 0.5 0 2010/2011 2011/2012 2012/2013 2013/2014 2014/2015 2015/2016 2016/2017 2017/2018 2018/2019 Season Summary: Control effective. Achillea ptarmica sneezewort No plants were found at existing sites apart from Husvik whaling station where stem and root fragments are spread during periods of flooding and plants continue to be found in flood areas. Spread is vegetative although in favourable seasons some plants will flower. 350 305 300 250 200 150 126 Coverage sq m sq Coverage 100 50 20.5 13.4 11.2 6 6.7 0 2012/2013 2013/2014 2014/2015 2015/2016 2016/2017 2017/2018 2018/2019 Season Summary: Control effective but continued vigilance for new fragments required. Non Native Plants on South Georgia Season Report 2018/19 Page 6 Agrostis stolonifera creeping bent The single site of 200 sq m in Husdal (near Husvik) was followed up this season. Spread is vegetative as the species is not known to flower or set seed at South Georgia. 250 200 200 150 100 Coverage sq m sq Coverage 50 1 0 2017/2018 2018/2019 Season Summary: Control effective. Agrostis vinealis brown bent Follow-up on all known sites was undertaken. More plants were found this year at sites normally trampled by fur seals (lower seal numbers this season resulted in less damage to vegetation, allowing plants to be more easily detected). Spread is both vegetative and via wind and water-assisted seed dispersal. 600 526.21 500 400 310.85 300 205.61 200 Coverage sq m sq Coverage 100 23.02 0 10 0.25 0 2010/2011 2011/2012 2014/2015 2015/2016 2016/2017 2017/2018 2018/2019 Season Summary: Control is effective on known sites however new sites are still being found. Non Native Plants on South Georgia Season Report 2018/19 Page 7 Allium schoenoprasum chives Nothing found at the Leith Harbour site this season. Spread is vegetative although the species was occasionally recorded in flower in favourable years. 0.12 0.1 0.1 0.08 0.06 0.04 Coverage sq m sq Coverage 0.02 0 0 0 0 0 2014/2015 2015/2016 2016/2017 2017/2018 2018/2019 Season Summary: Likely eradicated but site will still continue to be monitored. Anthoxanthum odoratum sweet vernal grass Sweet vernal grass occurs on the lower slopes of Husdal near Husvik, as well as at some small sites at Maiviken, Grytviken and Sorling. Plants, including outliers continue to be found at the Husdal site. Spread is via wind-assisted seed dispersal. 3500 3010 3000 2500 2001 2000 1500 Coverage sq m sq Coverage 1000 500 118.01 131.1 126.61 0 2014/2015 2015/2016 2016/2017 2017/2018 2018/2019 Season Summary: Control appears effective however seedlings keep appearing. Non Native Plants on South Georgia Season Report 2018/19 Page 8 Anthriscus sylvestris cow parsley The single site of this species is on the northern side of Nybrakka at Grytviken. Plants found were controlled before they flowered and produced seed; however, this site continues to produce seedlings from the original plant’s seedbank. Two new outliers were found this season up to 50m from the original plants showing the persistence of this species seedbank. 14 12 12 10 8 6 6 Coverage sq m sq Coverage 4 2 1 0.2 0.5 0.25 0.5 0.05 0.35 0 2010/2011 2011/2012 2012/2013 2013/2014 2014/2015 2015/2016 2016/2017 2017/2018 2018/2019 Season Summary: Control effective but persistent seedbank. Cardamine glacialis bittercress Three sweeps of the bittercress sites were completed this season with 4.3 sq m recorded. A new site was discovered across the cove 100m beyond the extent of previously known plants and next to the now disused walking track to the 1982 helicopter crash site. The higher number of seedlings this year is thought to have been due to the previous year’s exceptionally long and favourable growing season. Despite this, the total area controlled was less than last year . Detection of plants obscured by Acaena sp and Poa pratensis is still an issue; a first sweep in early spring before these 2 species have attained maximum growth and before fur seals have trampled plants should be considered.